Apparatus for flotation of minerals



Jan. 31, 1939. A, c. MUNRO ET Al.` 2,145,269

APPARATUS FOR FLOTATION OF MINERALS Filed Oct. 2, 19256 2 Sheets-Sheet lW (nm Jan. 31, 1939. A. c. MUNRO ET Al..

APPARATUS FOR FLOTATION 0F MINERALS Filed Oct. 2, 1956 2 Sheets-Sheet 2IN V EN TORS Werd/za@ ma, BYHu beni-"H PWS A T l RNEYS.

atented Jan. 3l, 1939 UNITED STATES APPARATUS FOR FLOTATION MNERALSAlexander C. Munro and Hubert A. Pearse, Britannia Beach, BritishColumbia, Canada Application October 2, 1936, Serial No. 103,703

7 Claims.

This invention relates to the separation of valuable constituents fromores or minerals byA a flotation process, and particularly by aflotation process of a type in which aeration of the pulp is effected byforcing air under pressure through a body of pulp in such manner as tocause the air to be distributed in the pulp under suitable conditions ofsubdivision andvdistribution for effective notation. In this type ofapparatus, sometimes referred to as the air-lift. or pneumatic fiotationapparatus, the air under pressure is generally introduced into a body ofpulp at a depth of between two and three feet. Our invention is' basedprimarily on the discovery that by introducing the air under pressure ata depth considerably greater than ordinarily used, for example, a. depthof about ten feet, a remarkable increase in flotation efficiency issecured, together with a decrease in the power required for a givenflotation capacity, and a more than proportional decrease in thehorizontal area of the apparatus for a given capacity.

One of the particular objects of the invention is to provide anapparatus which has a higher eapacity per square foot of floor spaceoccupied than has hitherto been obtainable in the air-lift or pneumatictype of flotation apparatus.

A further object of the invention is to provide a flotation apparatus ofthe air-lift or pneumatic type adapted to operate at a lower horsepowerconsumption and a. lower volume of air per ton of ore being treated thanhas hitherto been obtainable.

Our invention is particularly adapted to application to dotation cellsof the so-called "matless pneumatic flotation type (such as aredescribed in U. S. Patents No. 1,912,630 to Forrester and No. 1,732,893to Hunt), wherein air is introduced into a body of pulp through -aplurality thereof, or will be apparent from such descrip` tion. Theaccompanying drawings illustrate an advantageous embodiment of thepresent invention, and referring thereto:

Fig. 1 is a plan view of a flotation cell embodying our invention;

Fig. 2 is a section on line 2-2 in Fig. 1; and

Fig. 3 is a section on line 3-3 in Fig. 1.

The flotation cell illustrated in the drawings comprises a tank ortrough I having a fluid' supply means or feed inlet 2 at one end and auid discharge or tails outlet 3 at the other end. The feed inlet 2 maybe located at any desired point in one end wall of the tank, preferablybelow the `ing or varying the overiiow level.

pulp level, and the discharge outlet 3 may be located at any desiredpoint in the opposite end wall of the tank, preferably at a.considerable depth below the normal pulp level, said discharge outletcommunicating, for example, through a riser 4 with a tails launder 5,suitable adjustable means indicated at 6 being provided for adjust- Thetank I may be of usual or suitable dimensions as regards width andlength, but is of a depth considerably greater than the usual practice,being such as to provide a body of pulp not less than four feet andpreferably in the neighborhood of about ten feet in depth. Means areprovided for forcing air under pressure into the 4pulp contained in saidtank, said means comprising, for example, a header or air supply, pipe 1extending longitudinally over the center line of the tank and a seriesor plurality of vertical pipes or tubes 8 extending downwardly from theheader I and open at their lower ends. Said header communicates with anysuitable source of air or equivalent gaseous medium under pressuresuiiicient to overcome the submergence of the lower end of the pipes 8and cause air to be discharged into the body of pulp in the tank in suchmanner as to distribute the air in the form of bubbles, or a state ofiine subdivision, into the pulp.

Any suitable system of bailies may be used in I connection with the tankto control the circulation of pulp and froth, for example, verticalbai'-fles 9 may extend on opposite sides of the series of tubes 8 so as todefine an air-lift compartment I0 open at both lower and upper ends andextending to a level adjacent the lower end of the tank I, but spacedtherefrom. A defiecting baiiiel I is provided between the upper end ofeach baffle 9 and the adjacent side wall of the tank I. said bailies I Iextending from a point above the froth level to a point slightly belowthe upper ends of the baiiies 9. Suitable froth overflow lips arepreferably provided along the sides of the tank I,

as at I2, and suitable concentrate launders are provided as at I3 toreceive froth concentrate discharged over said lips.

The body of pulp within the tank I is maintained at the desired level bymeans of the tailings overiiow device shown at 6 in this particular formof apparatus, but it will be appreciated that any equivalentlevel-regulating means may be provided for the. purpose. In general,reference herein to introduction of air at a certain depth sol below thelevel or surface of the pulp will be understood to refer to the depthbelow the pulp or tailings overflow means or other equivalentlevelregulating means. Furthermore, it will be understood that the levelof the froth overow lips, such as I2, is adjacent or somewhat above thenormal pulp level, so that the depth of introduction of air, inaccordance with this invention,

is in excess of four feet, and preferably in excess of six feet, belowthe frothv overflow means, and that the preferred value of this depth isln the neighborhood of ten feet.

In the operation. of the apparatus the pulp, comprising nely divided oreor mineral, together with Water and a suitable froth notation agent, ispassed into the tank from the feed inlet 2 and in passing through thetank is subjected to aeration by the action of the air issuing inbubbles or finely divided form from the lower ends of the pipes 8. Theresulting mixture of pulp and finely divided air rises in the air-liftcompartment Ill (as shown by the ascending arrows in Fig. 2). In thisoperation, which produces a froth due to the presence of the flotationreagent, certain mineral values of the ore are separated from theremainder of the ore by selective action and become associated with thefroth, which passes under the baiiles Il and is discharged intoconcentrate launders I2. It will be appreciated that not all of thefloatable ore particles will be caused to enter the froth in a singlepath upwardly through the compartment I0, and such particles as have notentered the froth will be carried downwardly through the separating zoneof the tank, as defined by the portions of the tank outwardly of saidcompartment I0 (as indicated by the descending arrows in` Fig. 2), in arepetition of the flotation operation. Such particles as are not subjectto flotation are thus gradually worked longitudinally of the tank towardthe outlet 3,

thence to the discharge launders 5.

The so-called air-lift or pneumatic type of flotation machine hascertain inherent advantages over mechanical flotation machines, such aslow maintenance cost due to the absence of moving parts, while having arelatively low power consumption due to the use of low pressure air. Inthe conventional type of "matless pneumatic flotation machines now incommon, use, the depth of pulp maintained in a otation cell isrelatively shallow, being generally in the neighborhood of about 30inches, and the airwhich is introduced under pressure into the body ofpulp passes through a relatively shallow layer of pulp in contacttherewith for a relatively short time, and consequentlyalargepercentageof the air supplied escapes without doing any useful work. In view ofthe fact that the bulk of the matless pneumatic machines are of the samegeneral width, the capacity of such machine is conventionally expressedin terms of the length thereof, and it has been found that in theordinary type of such' pneumatic machine the volume of air required perlineal foot of machine varies from 50 to 80 cubic feet per minute (interms of free We have found that very material advantages can beobtained by considerably deepening the pneumatic type of machine, sothat'the depth of v pulp above the point of admission of the air isestablished at a height in excess of four feet, and preferably at aheight of six feet or more. In our preferred form of machine, the air isintroduced at a depth approximating ten feet, depths-much in excess often feet having been found to be but little more eectlve than ten footdepths, and not justifying the added cost of compression required tosupply the air at the greater depths. Not only does the same volume ofair come in contact with a much larger quantity of pulp than in ashallow machine, but also since the air is subjected to greater pressureat the point of admission, it is consequently more widely and uniformlydispersed through the pulp in the form -of smaller bubbles. As a resultof this more eiicient utilization of the air, we have found that amachine having air inlets submerged ten feet will treat nearly ve timesas much feed as eiiiciently as a machine of similar length and widthhaving air inlets submerged only approximately 30 inches. The volume ofair requiredis only one-fifth to one-sixth as much, but even though theair has to be supplied at a considerably higher pressure for the deepmachine, the actual consumption of power is less than half of thatrequired for the shallow cell.

We have found that a cell ten feet deep and ten feet long will treatapproximately 600 tons of ore per day and make the same metallurgicalrecovery of copper, iron, and gold as does a standard shallow matlesspneumatic type machine of the same width and 100 feet long treatingapproximately 1200 tons per day. On the particular ore employed in thesetests, the most advantageous air consumption of the standard shallowmachine was approximately 55 cubic feet per minute of free air perlineal foot of cell, or 5,500 cubic feet of free air per minute for athroughput of 1,200 tons per day. This air was required to be suppliedat a pressure of 1.9 pounds per square inch in the standard cell, whilein the cell of the present invention only 45 cubic feet of free air perminute were supplied per foot of length of the cell, at a pressureslightly less than 4.5 pounds per square inch.

As above pointed out, quantities of air ranging from 50 to 80 cubic feetper minute per lineal foot of machine are required in the conventionalmatless pneumatic apparatus, but it has been found that the deep cell ofthe present invention Will operate satisfactorily with air volumes aslow as 30 cubic feet per minute per foot of length and up to 60 cubicfeet per minute. Air volumes even lower than 30 cubic feet per minutehave been found quite adequate to maintain circulation and frothingwithin the apparatus, even with coarse feed, whereas the standardshallow pneumatic cell will tend to choke with air voliunes anywherenear comparable to this lower limit. The deep cell of the presentinvention thus appears to reach a maximum eiliciency with considerablylower air volumes than the shallow cell, and we have found that 45 cubicfeet per minute per foot of length is approximately the economicmaximum.

The following table sets forth comparative operating data on theabove-mentioned standard shallow matless pneumatic cell and a deep cellof the present invention:

Normal economic volume of air or free air rcquired for above pulp (perlineal foot of cell) (cu. ft./min.) 55 45 HP required per li n)cal footof cell (based on normal volume of a 0. 495 0, Lineal feet of cellrequired per ton of ore pcr hour 2 0. 4 Cubic feet ot free air requiredper ton of ore u, GUI) 1,080 HP hours required per ton of orc 0. 378

It may be pointed out that while the operating pressure required in thecell of ten foot depth is greater than that required in the cell of twoand one-half foot depth, the proportionate increasein pressure ismaterially less than the proportionate increase in depth. Thisdifference results primarily from the maintenance of a more thoroughlyaerated pulp column in the compartment i0 than is possible in theshallow type of cell, and the improved power eiiiciency and throughputcapacity of the present cell is Ia direct result of this more aeratedcondition of the pulp column, which condition may be maintained at alower volume of air per lineal foot of cell.

As may be seen from the above data, the pressure at which the gaseousmedium was supplied to the pulp, i. e., the -operating pressure of theapparatus, was less than the corresponding hydrostatic pressure of thepulp at the depth of submergence of the air inlet means. It will beappreciated that when a cell is started in operation, the air will haveto be introduced at a pressure sumcent to overcome the statichydrostatic pressure of the pulp, which pressure may be graduallyreduced to the desired operating pressure as the aerated pulp column isestablished in the aeration compartment.

The advantages of the deep machine may be summarized as follows:

A saving in power of about 60 per cent or more;

Only about one-fifth of the floor space required;

Somewhat lower initial cost, both for cells and blowing equipment, sincethe requirement displacement of the latter is so much smaller, eventhough higher pressure is necessary;

Less liability of the deep machine to choke on coarse feeds 4becausecirculation is positive and rapid. (The shallow air flotation cell nowin considerable use in the copper industry has not been acceptedgenerally in the lead-zinc operations, because o'f choking troubles andsluggish froth conditions with these ores of greater density; in orderto prevent chokingswith these ores,

of a moderately coarse grind, the wasteful practice of using abnormallyhigh air pressures for the shallow cell must be resorted to):

The deep machine is not so sensitive to slight changes in reagents,dilution and operating conditions, thus insuring a more positive frothdischarge and hence better mineral recovery;

With the more eilicient diffusion of air in the pulp, which results fromthe injection of higher pressure air, together with the longer contactof air and pulp, excellent otation conditions are obtained immediatelyat the head of the deep notation machine, whereas to get similarlydesirable results in the shallow cell, pulp conditieners ahead of`thecell are essential.

We have had successful results, as stated, with a machine operating withten feet submergence, but we desire it to be understood that greaterdepths may be used, if desired. However, we consider that ten feet isabout the limit to which the depth can be increased with practicaladvantages. Nor should it be assumed that it is necessary to reach eventen feet in depth in order to secure some benefit, since a machine onlysix or seven feet deep, or in any case over four feet, is more eiiicientthan one with an effective submergence of air inlets of only two andone-half to three feet. As a specific example of the increasedeiciencyof a relatively shallow cell of the present type over, that of. theconventional capacity of a standard cell with a thirty inch effectivesubmergence.

While the form of apparatus herein specifically described shows the useof drop pipes for introduction of the air for otation, it will beappreelated that any of the well-known equivalents for such drop pipesmay be substituted therefor without departing from the spirit or scopeof this invention. For example, a pervious bottom structure analogous tothat shown in U. S. Patent No. 1,547,548 (Allen et al.) may be employed;similarly, upwardly directed air supply openings or nozzles may beprovided below the compartment iii, such as are illustrated in U. S.Patent No. 1,441,560 (Connors); and in like manner, a perforated supplypipe may be extended along the lower portion of the compartment ld,after the manner of the'air inlet means shown at 61-62 in U. S. PatentNo. 1,912,228 (Shimrnin et al.).

1. A pneumatic or air-lift iiotation apparatus comprising: a tank; meansfor supplyingl pulp to said tank and for maintaining a body of said pulptherein; baffle means within said tank defining an air-lift compartmentand a separating compartment.; means for introducing gaseous medium intosaid tank below said air-lift compartment at a depth in excess of fourfeet below the surface of said body of pulp, the depth of submergencebeing such that the operating pressure required for operation of theapparatus is less than the hydrostatic head of the pulp at suchsubmergence; and means for overow of froth from said separatingcompartment.

2. A pneumatic or air-lift flotation apparatus comprising: a tank; meansfor supplying pulp to said tank and for maintaining a body of said pulptherein; baiile means within said tank denn-- ing an air-liftcompartment and a separating compartment; 'means for introducing gaseousmedium into said tank below said air-lift compartment at a depth inexcess of six feet below the surface of said body of pulp, the depth ofsubmergence of said gaseous medium introducing means being such that theoperating pressure required for operation of the apparatus is less thanthe hydrostatic head of the pulp at such submergence; and means yforoverflow of froth from said separating compartment.

3. A pneumatic or air-lift type flotation apparatus, which comprises: atank provided with lil lili

inlet means for mineral-bearing pulp, and outlet means for tailings:distributing means for delivering a 'gaseous medium into the tank at asubmergence of over four -feet in the pulp; means Ai'or supplying agaseous medium to said distributing means at such pressure as toovercome such submergence and to cause such gaseous medium to issue innely divided form from the distributing means into the pulp, overflowlaunder means at the side of the tank for carrying off froth otationconcentrates, and baille means in the tank for controlling the flow offroth to the con'- centrates overflow, the depth of submergence beingsuch that the operating pressure required for operation of the apparatusis less than the hydrostatic head of the pulp at such submergence.

4. A pneumatic or "air-lift" type flotation apparatus, which comprises:a tank provided with inlet means for mineral-bearing pulp, and outletmeans for tailings; distributing means for delivering a. gaseous mediuminto the tank at a submergence of over six feet in the pulp; means forsupplying a gaseous medium to said distrib uting means at such pressureas to overcome such submergence and to cause such gaseous medium toissue in nely divided form from the distributing means into the pulp,overflow launder means at the side of the tank for carrying off frothotation concentrates, and baille means in the tank for controlling theflow of froth to the concentrates overow, the-depth of submergence beingsuch that the operating pressure required for operation of the apparatusis less than the hydrostatic head of the pulp at such submergence.

5. A pneumatic or air-lift type flotation apparatus, which comprises: atank provided with inlet means for mineral-bearing pulp, and outletmeans for tailings; distributing means for delivering a gaseous mediuminto the tank at a submergence of approximately ten feet in the pulp,means for supplying 4gaseous medium to said distributing means at suchpressure as to overcome such submergence and to cause such gaseousmedium to issue in finely divided form from the distributing means intothe pulp, overflow launder means at' the side of the tank for carryingoi froth flotation concentrates, and

bale means in the tank for controlling the flow of froth to theconcentrates overflow.

6. A pneumatic or air-lift flotation apparatus, which comprises: a tankadapted to hold a body of pulp comprising mineral-bearing solids influid suspension; uid supply means for delivery of pulp to said tank;fluid discharge means for withdrawal of pulp from said tank andincluding means for maintaining a fluid level of pulp within said tank;a source of gaseous medium under pressure; distributing means associatedwith such source of gaseous medium for delivering the same underpressure into said body of pulp at a depth of approximately ten feetbelow said fluid level, such pressure being sulficientn to cause suchgaseous medium to issue in nely divided form from said distributingmeans; and overflow launder means for said tank for carrying oi frothflotation concentrates.

7. A pneumatic or air-lift flotation apparatus which comprises: ahorizontally elongated tank adapted to hold a body of pulp comprisingmineral-bearing solids-in fluid suspension; fluid supply means adjacentone end of said tank for delivery of pulp thereto; fluid discharge meansadjacent the other end of said tank for withdrawal o1 pulp therefrom andincluding overilow means for maintaining a fluid level within said tank;baffle means extending longitudinally of said tank and defining anair-lift compartment therewithin extending vertically downwardly fromabove said fluid level to a level adjacent but spaced from the bottom ofsaid tank; a source of gaseous medium under pressure; distributing meansassociated with such supply of gaseous medium for delivering the sameunder pressure into said body of pulp at a point adjacent the lower endof said air-lift compartment and at a depth of approximately ten feetbelow said fluid level. such pressure being sufcient to cause suchgaseous medium to issue in finely divided form from said distributingmeans; and overflow launder means at the side of said tank for carryingoff froth flotation concentrates.

ALEXANDER C. MUNRO. HUBERT A. PEARSE.

